Series double break rod array vacuum switch

ABSTRACT

A series double break vacuum switch includes a pair of main electrodes and at least one, but preferably at least two, secondary electrodes juxtaposed in a radial array of parallel spaced rods within a switching chamber. Main electrodes enter the arcing chamber through one longitudinal end and secondary electrodes are interconnected by a common conductive mounting member at the opposite end of the switching chamber. The arrangement and connection of the main and secondary electrodes facilitates &#39;&#39;&#39;&#39;blow out&#39;&#39;&#39;&#39; of initial arc to extended area gaps between main and secondary electrodes and causes current flow in such direction within switch to prevent formation of destructive anode spots.

United States Patent Rich [54] SERIES DOUBLE BREAK ROD ARRAY 1 Feb. 15,1972

FOREIGN PATENTS OR APPLICATIONS VACUUM SWITCH 196,960 5/1967 U.S.S.R. ..200/|44 a [72] Inventor: Joseph A. Rich, Schenectady, NY.

Primary Examiner-Robert S. Macon Asslgneei General Electric Company Attorney.lohn F. Ahern, Paul A. Frank, Richard R. 22 F] d: Dec. 10, 0 Brainard, Jerome C. Squillaro, Frank L. Ncuhauser, Oscar B. I 1 e 197 Waddell and Joseph B. Forman [21] Appl. No.: 96,769

[57] ABSTRACT [52] 0.8. CI ..200/l44 B A series double break vacuum switch includes a pair of main [51] Int. Cl. H01h 33/66 electrodes and at least one. but preferably at least two, secon- [58] Field of Search 200/144 B dary electrodes juxtaposed in a radial array of parallel spaced rods within a switching chamber. Main electrodes enter the [56] References Cited arcing chamber through one longitudinal end and secondary electrodes are interconnected by a common conductive UNITED STATES PATENTS mounting member at the opposite end of the switching chamber. The arrangement and connection of the main and Jennings "I. B Secondary electrodes blow of arc to 3,071,667 Lee B tended-area g p between main and secondary electrodes m 3'156'803 11/1964 Sonny et "200/144 B causes current flow in such direction within switch to prevent 3,283,101 11/1966 Cobme et al. .....200/ 144 B formation destructive anode spots 3,336,664 8/1967 Hawkins ....200/144 B X 3,509,404 4/1970 Rich ..200/ 144 B 10 Claims, 2 Drawing Figures 2 a I I I I v 2 1 I4 I 7 l6 l7 7 7 4/4 {ii 1 4 3 j 4 1 3 y :1 /Q :1 Z j 7 2 2 2 4 I 1 7 2 m y 7 1 I l8 a I\\\\\\\\\\Yl in! 24 l? 51 UH 22 1| 1 I 33 '1 J i], 1 1i 23 IF; i [Q s 1 Q PATENTEDFEB 15 1912 3, s43 047' //V l E/V TOR: JOSEPH A. R/ H,

H/S ATTORNEY SERIES DOUBLE BREAK ROD ARRAY VACUUM SWITCH This invention relates to series double break vacuum switches. More particularly, the invention relates to such switches as contain electrode configurations and interrelationships which optimize the transfer of arching current from interrupter gaps to are extinction gaps of extended area and also to permit the carrying of high-arcing currents without the formation of destructive anode spots.

It has been known in the voltage switching arts that the voltage hold-off" characteristics of the circuit interrupter system may be greatly increased by the use of two arcing gaps in series. Generally, the voltage holdoff characteristic may be described as that voltage which may be withstood by an opened switching system under failure conditions, once a circuit interrupting arc has been struck and extinguished, without having the arc restrike, with the arc electrodes separated. Similarly, it has been known that the current carrying capacities of interrupting systems may be improved by the use of two arching gaps in parallel. The use of multiple arcing devices in separate enclosures in well known,but is wasteful of space, is expensive, and raises problems of simultaneous actuation which require intricate circuitry. With the advent of vacuum are devices, the incorporation of multiple gapped devices within the same evacuated container has become feasible. With such combination, however, as for example that shown in Cobine et al. U.S. Pat. No. 3,283,101, the problems of avoiding the concentration of current density which causes destructive anode spots is increased. Such problems have been faced and have been largely controlled by my previous work, as for example, by the improvements set forth in my US. Pat. Nos. 3,471,733; 3,471,743; and 3,471,736 in the environment of a single vacuum gap in a given chamber.

The introduction of a plurality of arcing gaps within the same chamber to achieve the advantage of plural gaps, however, introduces problems of separation of switching actions, for example, of magnetic interaction with arcing currents, not present in the rather simplified devices incorporating a single gap within a single envelope. Such problems have heretofore prevented the successful commercial realization of the theoretical advantages of plural vacuum gaps in the same chamber.

Accordingly, it is an object of the present invention to provide a plural gap vacuum switch wherein at least two arcing gaps are located within the same vacuum enclosure.

Another object of the present invention is to provide a series double break vacuum switch device wherein the configuration and interrelationship of arc electrodes within a single envelope avoids harmful interaction between magnetic forces and arcing currents.

Briefly stated, in accord with one embodiment of the invention, 1 provide a pair of main electrodes and at least one, but preferably at least two, secondary electrodes associated with each main electrode, all located in parallel spaced relationship within the arcing chamber of a single vacuum enclosure. The main electrodes are insulatingly passed through the same longitudinal end of the vacuum chamber and the secondary electrodes are all connected to a common conducting member at the opposite longitudinal end of the arcing chamber. A bridging electrode makes a circuit closing contact with the main electrodes. When the bridging contact is moved to a circuit-open position, plural series arcs are established between each of the main electrodes and respective portions of the bridging electrode. The configuration and the interrelation ship of the electrodes causes the initial arcs to be magnetically impelled outwardly therefrom so as to dwell between the main and secondary electrodes in an extended area gap. Due to the electrode arrangement, the current in adjacent main and secondary electrodes is in the same direction, so that the net gross magnetic field thereat is azimuthal, with respect to the switch, and no arcing current bunching occurs.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itchamber defined by a substantially cylindrical side wall member 11 and a pair of substantially planar end wall members 12 and 13. A pair of parallel spaced main electrodes 14 and 15 extend through apertures in the same end wall member 13 of switch 10 and are disposed in parallel spaced relationship with at least a pair of secondary electrode members 16 and 17 which are electrically and mechanically affixed to opposite end wall member 12 and define, with main electrodes 14 and 15, extended area gaps. Although not visible in the drawing, a second pair of secondary arc electrodes 19 and 20 may also be disposed in parallel spaced relationship with main electrodes 14 and 15 on the opposite lateral side thereof and may also be affixed electrically and mechanically to end wall member 12. A bridging electrode 18, which is a functionally flat conductive member is supported upon a bridging electrode support member 21, which contains an electrically insulating section 22 and which is connected with a hermetically sealed bellows assembly 23, serves as circuit interrupting means for the device. In the closed circuit position illustrated in H6. 1, bridging electrode 18 is in contact-making position with the inwardly disposed ends of main electrodes 14 and 15. The ends of electrodes 14 and 15 are smoothly rounded at the peripheries thereof to remove any sharp corners or edges which might cause conduction currents to bunch and cause intolerable concentration of arcing currents, but the end portions thereof are sufficiently flat as to make a reasonably broad area contact with bridging electrode 18, also to maintain low-current density at the regions at which the starting arcs are initiated.

An actuating rod 32 actuates bridging electrode 18 to cause initial arcs to be struck between bridging electrode 18 and each of main electrodes 14and 15. Since end wall member 12 must be apertured in order to allow support rod 21 to extend therethrough, the lower chamber 33 surrounding bellows 21 is also in communication with the arcing chamber defined by members 11, 12 and 13. Accordingly, insulator 20 must be protected from the deposition thereupon of arc-supporting specie which would short out the same and cause the actuator rod 32 to be connected to an operating voltage. This is avoided by downwardly depending flange 24 which is affixed to bridging electrode support 21 and upwardly depending flange 25 which is affixed to bellows assembly 23, which flanges in combination comprise an effective shield for insulator 21. Since side wall member 11 is connected substantially across opposite ends of the device it is generally advisable that it be constructed of an insulating member, as for example Pyrex glass, and that it be protected from the deposition of specie evolved from the arcing electrodes to prevent short circuiting thereof. Such isolation is provided by a cylindrical, longitudinally disposed shield member 29 which is supported by a flange imbedded in a bead located along the interior of side wall member 11. Shield 29 has no particularly identifiable electrical potential, but is electrically floating.

Main electrodes 14 and 15are physically supported from a pair of electrode support rods 26 and 27 which extend through insulating bushings 28 and are hermetically sealed thereby to upper end wall member 13 to complete the hermetic sealing of the evacuable envelope of switch 10. The ends 30 and 31 of rods 26 and 27, respectively constitute a pair of main terminal means for connection of the switch 10 in circuit with an electric load which is to be switched or interrupted by the action of switch 10.

Since, in operation, the switch 10 is generally operated with an initial vacuum of approximately the order 10 torn, and since exceedingly high temperatures are created by the establishment of a very high-current arc therein, it is required that the electrodes be of very high-purity material so that no permanent destruction of the vacuum therein is caused by the evolution of sorbed gases from any materials exposed to the arc discharge. Accordingly, rod electrodes l4, l5, 16, 17, 19 and 20 and bridging electrode 18 and possibly even end wall members 12 and 13 and rods 26 and 27 are usually fabricated of a material which is highly purified as, for example, by vacuum melting or by repeated zone refining to limit residual impurities to the order of a few parts per million or less. Also, since the conducting specie which sustains an electric arc in the operation of the device is metal vapor evolved from the g are electrodes, the electrodes should all be fabricated from a material having a vapor pressure at least as high as that of copper and preferably a suitable high vaporpressure metal or alloy which, in addition to having good high-vapor pressure characteristics, also has poor welding characteristics. Preferably any of the materials set forth in US. Pat. Nos. 2,975,256 Lee et al.; 2,975,255 and 3,016,434 Lafferty: and 3,140,373 and 3,497,755 Horn, for example, are suitable and may be used in forming electrodes in accord with the present invention.

Shield 29 does not take part in the arcing process and, although required tobe free of sorbed contaminants, need not be a high vapor pressure material. It may be conveniently made of nickel or stainless steel which is repeatedly heated at high temperature in order to remove all sorbed gases therefrom.

Topologically, the device of FIG. 1 illustrates a pair of series connected, normally closed switches, each having a starter gap and a plurality of extended area arcing gaps which are between an adjacent main electrode and its associated secondary electrodes. In order that the switching characteristics of the two sets of electrode gaps are able to operate independently, although in the same vacuum enclosure, it is in some circumstances desirable to separate the two sets of switches from one another, so that conducting specie evolved from one do not migrate to the other, field possible deleterious effects, although both gaps should be conducting or nonconducting at the same time. Such an optional barrier is provided in the form of a metallic planar plate 34, which is interposed between main electrodes 14 and 15, and is suspended from end wall abutt 13.

An essential feature of the invention lies in the cylindrical, rod-shaped configuration of primary and secondary electrodes 14, 1 5, 16, 17, 19 and 20. Each of the adjacent electrode pairs 1416. 14-19, 15-17 and l- 20, comprise a pair of adjacent cylindrical members wherein the arcing surface of each member is a smooth semicylindrical section, so that broad area arcing surfaces are provided to facilitate the diffusion of the cathode and anode foot points over a large area and maintain a low-current density,even though high current may be carried. It is also imperative that such configuration be utilized in order to avoid sharp or pointed edges or corners at which magnetic forces tend to cause bunching of arcing currents and at which electrostatic forces tend to cause unusual field concentrations which also favor high current densities thereat. It

trodes are smoothly rounded so as to remove sharp edges while still maintaining, particularly for main electrodes 14 and 15 a sufficiently flat surface to abut with bridging electrode 18 and form a broad area contact.

The topology of the device of FIG. 1 is illustrated by the plan view of FIG. 2 which is a cross-sectional view through the arcing chamber of the device of FIG. 1 and illustrates the juxtaposition of primary electrode 14 with secondary electrodes 16 and 19 and defining therewith extended area gaps 35. Similarly, main electrode 15 defines respective broad area arcing gaps 35 with secondary electrodes 17 and 20. The distance between the associated primary and secondary electrodes is sufficientlysmall in relation to the other dimensions of the device such that, in the fully retracted position, bridging electrode 18 is a greater distance away from primary electrodes l4 and 15 than the distance between primary electrodes l4 and 15 and their respective secondary electrodes-16 and 19, on one hand, and 17 and 20 on the other hand, This facilitates the rapid transfer to the broad area arcing gaps of the initial arcs struck between the inwardly depending ends of main electrodes 14 and 15 and the bridging electrode 18 due to the lower arc voltage thereat. Additionally, the fact that the initial arcing current is passing through a change in direction in passing between the main electrodes and the bridging electrode causes a blow-out" efi'ect which rapidly tends to propagate the initial arc radially outward. Thus, the combination of magnetic blow-out" of the initial interruption gaps and the small distance between the main and secondary electrodes, as compared with the fully retracted gap length between the main and the bridging electrodes, almost instantaneously causes the arc struck upon interruption to be transferred to the extended area gaps 35 at which the arcs burn over a large area without the formation of anode spots of very high-current densities until a current zero is encountered, at which time the arcing chamber is deionized and the arc is extinguished. Since the gaps are at that time open, the arc is not restruck as the voltage is built-up on the next alternating half cycle.

It is at this point that the advantage of the double break vacu'um switch becomes evident. In general, the arc is not struck between the arc electrodes unless a fault has occurred and an overvoltage exists between the main electrodes. The actuation of the bridging electrode is effected in order to interrupt the current and protect electrical apparatus against such overvoltage. Generally, the overvoltage. persists even though the arc is interrupted and there is, consequently, a great tendency for the arc to restrike after a current zero" is encountered when the next half cycle of the alternating voltage is applied across the opened gaps of the vacuum switch. Since, in the double break series vacuum switch, there are two gaps in series, the holdofi' voltage of such device is, in essence, double that which one would find in a single gap vacuum switch. j

Heretofore, it has not been possible to provide a pluralseries break vacuum switch because the criteria of maintaining freedom from destructive anode spots was only worked out for the instance of a single arcing gap within asingle container. In

accord with the present invention, the juxtaposition and shaping of the arcing electrodes is such as to preclude the formation of destructive anode spots and favor the maintenance of low-current densities in the device. I

The foregoing is accomplished in the present invention by the shaping and the positioning of the electrodes as described herein. As is mentioned hereinbefore, the shaping of the electrode so as to have no sharp corners or edges and to provide broad area contacts between abutting semicylindrical surfaces optimizes the current carrying capacity of the arcing gaps 35. Similarly, the location of both main electrodes with current feed in the same direction, with a transverse current path, as is obtained by passage of current between the two sections, those respectively associated with main electrodes 14 and 15, is such that the magnetic field generated by current passage through the switch leaves a substantially net azimuthal magnetic field in the vicinity of the arcing gaps 35. Such magnetic fields do not allow any JXB vector'product to cause the action of a body force upon the arcing currents to cause bunching thereof and the formation of destructive anode spots. To understand better the foregoing, consider FIG. 2 of the drawing. After the initial arcs have been struck and have been transferred from the interrupting gaps at bridging electrode 18 and transferred to gaps 35, current maybe assumed to flow into the switch at electrode 14 and out of the switch at electrode 15. Thus, current is directed downwardly into electrode 14 (and into the drawing) in FIG. 2 and out of the switch (and out of the drawing) at electrode 15. Due to the connection of the main and secondary electrodes, current is directed into the drawing in secondary electrodes 16 and 19; from electrode 16 to electrode 17 on one hand; and from electrode 19 to electrode 20 on the other hand, both paths through end wall member 12. The current path is then directed upwardly in electrodes 17 and 20, is transferred across gap 35 to electrode and therefrom, passes out of the switch. It may be seen therefore, that the current paths are in the same direction in the arcing electrodes on either side of each of gaps 35. This results in a net cancellation of magnetic fields between the rods resulting in the gaps 35 being magnetically field-free, leaving only the gross azimuthal magnetic fields about the array, which are parallel with the arcing current paths and have no effect thereupon. Similarly, in the gaps between are electrodes l4 and 19 and 14 and 16, the same cancellation occurs. Current paths between electrodes 19 and on one hand, and 16 and 17 on the other hand, are between electrodes which have no current therebetween. Furthermore, the effects of this current does not create magnetic fields which extend outwardly to the other interelectrode gaps. Thus, due to the geometry of the electrodes per se, the juxtaposition of the electrodes within the device, and the current feed characteristic of the device, the possibility of interaction of transe verse arcing currents and magnetic field resulting in a J B vector product is eliminated in accord with the invention.

Devices constructed in accord with the present invention, as indicated hereinbefore, are utilized to be connected in circuit with, and preferably in series with, an electric load to protect against overvoltage in an alternating current load. The devices are operative to interrupt the applied voltage upon the occurrence of an overvoltage signal. Once such an interruption has occurred, the holdoff voltage against restriking an are due to the presence of the overvoltage is substantially increased, theoretically by a factor of two, thus producing devices able to withstand higher overvoltages for the same general size and voltage of current rating.

The devices in accord with the present invention are able to interrupt and maintain in the interrupted state, voltages of the order of 50 and 100 kilovolts carrying currents of the order of 50,000 amperes to 100,000 amperes (peak).

While the invention has been set forth herein with respect to certain specific embodiments and examples, it is readily apparent that any modifications and changes will readily occur to those skilled in the art. Accordingly, I intend, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A series double break vacuum switch comprising:

a. an hermetically sealed envelope evacuated to a pressure of approximately 10 torr or less and including a switching chamber;

b. a pair of cylindrically shaped rodlike main electrodes extending in parallel spaced relation within said envelope and terminating in smooth surfaced ends in a first transverse plane near one longitudinal end of said switching chamber;

. at least one cyclindrically shaped rodlike secondary electrode closely juxtaposed in spaced relation to each of said main electrodes, affixed electrically and mechanically to a conducting member at said one longitudinal end of said switching chamber and terminating in smooth surfaced ends substantially in a second transverse plane near the remaining longitudinal end of said switching chamber and defining with the associated main electrode an extended area arcing gap; v

d. a longitudinally reciprocable bridging electrode disposed at said one longitudinal end of said switching chamber and movable between a first closed-circuit position bridging said smooth surfaced ends of said main electrodes and a second open-circuit position defining an arcing gap with the smooth surfaced end of each of said main electrodes, and

e. terminal means at said second longitudinal end of said switching chamber for insulatingly passing electrical contacts to each of said main electrodes through said hermetically sealed envelo e.

2. The switch of claim wherein at least two secondary electrodes are juxtaposed in spaced relation to each of said main electrodes.

3. The switch of claim Zwherein said main and said second'ary electrodes are arrayed in said chamber equidistant from the longitudinal axis thereof forming a circular electrode array.

4. The switch of claim 1 wherein means are disposed between one of said main electrodes and the secondary electrodes associated therewith on one hand, and the other set on the other hand, to prevent direct passage of ionized species between the extended area arcing gaps associated with respective main electrodes.

5. The switch of claim 4 wherein said means comprises a metallic baffle plate electrically connected with said envelope.

6. The device of claim 4 wherein the distance between said bridging electrode and said main electrodes in open-circuit position is greater than the spacing between said main electrodes and said secondary electrodes along said extended area arcing gap.

7. The switch of claim 4 wherein actuation means for said bridging member bridging member is provided to resiliently move said bridging member between said open circuit position and said closed circuit position and a bellows mechanism therefor maintains vacuum integrity.

8. The switch of claim 4 wherein said main and said secondary electrodes have smoothly rounded cylindrical surfaces so that the arcing surface of each which sustains an arc with an adjacent electrode comprises essentially a smooth semicylindrical surface.

9. The switch of claim 8 wherein during arcing when said bridging electrode is in open-circuit position, the magnetic fields existing in the vicinity of said main electrodes are substantially azimuthal.

10. The switch of claim 4 wherein said main and said secondary electrodes comprise a metallic material having a vapor pressure at least as high as that of copper. 

1. A series double break vacuum switch comprising: a. an hermetically sealed envelope evacuated to a pressure of approximately 10 5 torr or less and including a switching chamber; b. a pair of cylindrically shaped rodlike main electrodes extending in parallel spaced relation within said envelope and terminating in smooth surfaced ends in a first transverse plane near one longitudinal end of said switching chamber; c. at least one cyclindrically shaped rodlike secondary electrode closely juxtaposed in spaced relation to each of said main electrodes, affixed electrically and mechanically to a conducting member at said one longitudinal end of said switching chamber and terminating in smooth surfaced ends substantially in a second transverse plane near the remaining longitudinal end of said switching chamber and defining with the associated main electrode an extended area arcing gap; d. a longitudinally reciprocable bridging electrode disposed at said one longitudinal end of said switching chamber and movable between a first closed-circuit position bridging said smooth surfaced ends of said main electrodes and a second open-circuit position defining an arcing gap with the smooth surfaced end of each of said main electrodes, and e. terminal means at said second longitudinal end of said switching chamber for insulatingly passing electrical contacts to each of said main electrodes through said hermetically sealed envelope.
 2. The switch of claim 1 wherein at least two secondary electrodes are juxtaposed in spaced relation to each of said main electrodes.
 3. The switch of claim 2 wherein said main and said secondary electrodes are arrayed in said chamber equidistant from the longitudinal axis thereof forming a circular electrode array.
 4. The switch of claim 1 wherein means are disposed between one of said main electrodes and the secondary electrodes associated therewith on one hand, and the other set on the other hand, to prevent direct passage of ionized species between the extended area arcing gaps associated with respective main electrodes.
 5. The switch of claim 4 wherein said means comprises a metallic baffle plate electrically connected with said envelope.
 6. The device of claim 4 wherein the distance between said bridging electrode and said main electrodes in open-circuit position is greater than the spacing between said main electrodes and said secondary electrodes along said extended area arcing gap.
 7. The switch of claim 4 wherein actuation means for said bridging member bridging member is provided to resiliently move said bridging member between said open circuit position and saId closed circuit position and a bellows mechanism therefor maintains vacuum integrity.
 8. The switch of claim 4 wherein said main and said secondary electrodes have smoothly rounded cylindrical surfaces so that the arcing surface of each which sustains an arc with an adjacent electrode comprises essentially a smooth semicylindrical surface.
 9. The switch of claim 8 wherein during arcing when said bridging electrode is in open-circuit position, the magnetic fields existing in the vicinity of said main electrodes are substantially azimuthal.
 10. The switch of claim 4 wherein said main and said secondary electrodes comprise a metallic material having a vapor pressure at least as high as that of copper. 